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Principles of Science > Anaesthesia Maintenance > Flashcards

Anaesthesia Maintenance Flashcards

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1
Q

What should be done when intubating?

A

Sufficient depth of anaesthesia - eyes rotated ventrally, minimal, sluggish palpebral reflex, loose haw tone, no swallowing reflex on stimulation
Pull tongue out and use laryngoscope - don’t touch epiglottis or larynx
Visualise laryngeal opening
Local anaesthesia
Lubrication

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2
Q

How do you measure for endotracheal tube size?

A

Measure from mouth to point of shoulder

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3
Q

Describe some problems that can occur with endotracheal tubes

A

Occlusion of end of ET tube - can be prevented with Murphy’s eye
Endobronchial intubation
Compression of inside of tube
Stretching of tracheal wall
Mucus in tube - risk of occlusion and infection

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4
Q

Describe intubation in cats

A

Spray larynx with local anaesthetic - desensitise, reduce laryngospasm during intubation
Intubease - lidocaine spray
Easy to overdose - take care of local anaesthetic toxicity
Alternative options - V-gel, laryngeal mask

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5
Q

What six things are involved in balanced anaesthesia

A 
Minimization of stress
Analgesia
Muscle relaxation
Decrease amount of drugs used
Minimize autonomic reflex activity
Unconciousness
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6
Q

What two things are dose-dependent with anaesthetic agents?

A

Cardiovascular depression - decrease in cardiac output, vasodilation, reduced blood pressure
Respiratory depression - decreased respiratory rate, decrase tidal volume, reduced minute volume

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7
Q

What do most general anaesthetics not provide?

A

Analgesia

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8
Q

What is the one anaesthetic that does provide analgesia?

A

Ketamine

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9
Q

Why is analgesia still required when patient is unconscious?

A

Prevent upregulation of pain processing pathways

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10
Q

What are the four common routes of anaesthesia administration?

A

Inhalational
Intravenous - TIVA, intermittent boluses, CRI
Combination of injectable and inhalational - balanced techinques, PIVA
Intramuscular - single sufficient, darting wild or zoo animals

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11
Q

What are four examples of injectable anaesthetics?

A

Propofol
Alfaxalone
Ketamine
Thiopental

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12
Q

What are six examples of inhalational anaesthetics?

A 
Isoflurane
Sevoflurane
Halothane
Desflurane
Nitrous oxide
Xenon
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13
Q

What is the one inhalational agent that isn’t administered and removed by the lungs?

A

Halothane

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14
Q

How do inhalational anaesthesia agents work?

A

From alveoli
Agent absorbed into blood
Travel up to brain
Induce effects

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15
Q

Where can inhalational agents redistribute?

A

Into other tissues - fat

Fat solubility may slow recovery from long anaesthetic

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16
Q

What factors affect inhalational agent uptake?

A

Pressure gradient from vaporizer to brain - vaporizer, anaesthetic circuit, alveoli, blood, brain
Brain concentration approximates alveolar concentration

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17
Q

What factors affect the speed of induction?

A

High partial pressure in lungs equals high partial pressure in brain
Agents soluble in blood will have lower partial pressure in lungs - lower partial pressure in brain
Speed of induction slower for more soluble agents - also recovery

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18
Q

Describe the blood/gas partition coefficient

A

Number of parts of gas in blood vs. alveolus
High number means gas is very soluble in blood
More soluble agents are slower to change depth of anaesthesia during maintenance

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19
Q

Give the five main inhalational agents in decreasing partition coefficient

A 
Halothane
Isoflurane
Sevoflurane
Nitrous oxide
Desflurane
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20
Q

What is the MAC?

A

Minimum alveolar concentration - amount required to prevent movement in response to pain in 50% of animals

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21
Q

What concentration should be aimed for in clinical anaesthesia?

A

1.25-1.5 times MAC

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22
Q

What does the MAC depend on?

A

Other agents also administered

Species

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23
Q

What factors influence MAC?

A

Decreases - hypothermia, very young, older, severe hypoxia/hypercapnia, severe hypotension, CNS depressant drugs, pregnancy
Increases - hyperthermia, young, fit, excitation

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24
Q

What is MAC not affected by?

A

Length of anaesthesia
Gender
Blood pH

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25
Q

Give MAC values for the dog, cat and horse with isoflurane and sevoflurane

A

Dog - isoflurane 1.3, sevoflurane 2.3
Cat - isoflurane 1.6, sevoflurane 2.6
Horse - isoflurane 1.3, sevoflurane, 2.3

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26
Q

What are the differences and similarities with anaesthetic agents?

A

Cardiovascular depression leading to reduced blood pressure - mainly with halothane, some with iso/sevo
Respiratory depression - similar for all
Liver metabolism - around 20% in halothane, lower in others

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27
Q

Describe sevoflurane metabolism

A

Theoretically free fluoride ions released - toxic to kidney, though no problems reported clinically
Compound A formed during reaction with hot and dry carbon-dioxide absorber - nephrotoxic, newer absorbers prevent this
Low flow anaesthesia potentiates these processes

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28
Q

Describe isoflurane

A 
Vasodilation
CV depression
Cheaper
Stronger smell
Patient less compliant
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29
Q

Describe sevoflurane

A 
Less CV side effects than Iso
Maintains cerebral perfusion better than Iso
More expensive
Better tolerated
Less irritant
Compound A - reaction with CO2 absorbant
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30
Q

Describe Nitrous oxide

A

MAC in animals around 200%
Cannot be used as sole agent - hypoxia
Mild analgesic properties
Very insoluble
Very fast onset
Can speed onset of another agent - second gas effect
Less important now that insoluble agents are routinely used
Need diffusion hypoxia at end of anaesthetic - diffuses rapidly into lungs, reduces partial pressure of oxygen in lungs
Health risk with long term exposure
Atmospheric pollution

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31
Q

When does most aneasthetic mortality occur?

A

Recovery period

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32
Q

When should extubation be done?

A

When swallowing reflex returns
Cats slightly earlier to prevent laryngospasm
Later if concerned about airway protection - brachycephalic dogs, vomiting risk, ruminants

33
Q

What should be done doing recovery?

A

Continue monitoring - heart rate, respiratory rate, temperature
Oxygen administration if necessary
Fluid therapy if necessary
Temperature
Post-operative analgesia
Nursing care and TLC - empty bladder, comfortable bandages

34
Q

What are the main goals with anaesthesia monitoring?

A

Make sure all components of balanced anaesthesia are provided for
Maintain homeostasis as best as possible
Detect any adverse effects of anaethesia

35
Q

What should you try and adopt when monitoring?

A

Methodical, structured way of monitoring

Patient - monitoring equipment - anaesthetic machine - fluids

36
Q

What should be logged on an anaesthetic record?

A

Time, dose and route of drugs given
All intra-operative monitoring every 5 minutes
Iv fluids given - rate, type
All procedures performed
Time of important events - induction, positioning, start of surgery, extubation
Unusual events or complications
Condition of animal at the end of the procedure

37
Q

How can blood volume be calculated with dogs and cats?

A

80ml/kg for dogs

60ml/kg for cats

38
Q

When should we note blood loss?

A

When it is equal to 10%, 15% and 20% of blood volume

Helps decision making on whether crystalloids, colloids or blood are likely to be needed

39
Q

What should be clinically observing when monitoring anaesthesia?

A 
Depth of anaesthesia
Mucous membranes
Pulse
Chest movements
Pupil size
Response to surgery
Blood loss
Urine output
40
Q

What should we be using monitoring equipment to monitor during anaesthesia?

A 
Respiratory gases
Pulse oximeter
Blood pressures
ECG
Thermometer
Blood gases
41
Q

Why is it important to check cylinder pressure and oxygen flow meters constantly?

A

Some machines may not have low oxygen warning alarms fitted

42
Q

How can you ensure you are not delivering an hypoxic mixture to the patient?

A

Check oxygen/nitrous oxide ratio on a regular basis

Only really necessary when using nitrous oxide

43
Q

What things should be monitored on the equipment during anaesthesia?

A 
Cylinder pressure
Oxygen flow meters
Oxygen/nitrous oxide ratio
Vaporizer settings
Level of volatile anaesthetic in vaporizer
Breathing system - operation, disconnection
Rate of fluid administration
Contents of fluid bags
44
Q

How does monitoring equipment help with anaesthesia?

A

More detailed information
Early warnings
Helps reduce morbidity and mortality

45
Q

How can we assess the depth of anaesthesia?

A 
Cardiovascular responses to stimulation - heart rate, blood pressure
Respiratory changes - rate, tidal volume
Eye position
Nystagmus
Lacrimation
Pupil size
Response to light
Neurological responses - cranial nerve reflexes, other reflexes
Muscle relaxation
EEG changes
46
Q

What physiological parameters do we continually assess in anaesthesia patients?

A

Heart rate
Pulse - rate and quality
Respiration - rate, character, quality
All particularly in response to painful stimuli

47
Q

What is a simple way to monitor the heart and breathing?

A

Oesophageal stethoscope - inexpensive, non-invasive

48
Q

What does a capnograph do?

A

Measures CO2 in respiratory gases
Continuous
Non-invasive

49
Q

How does a capnograph estimate partial arterial pressure?

A

End tidal carbon dioxide

Approximately partial arterial carbon dioxide

50
Q

What are the normal ranges for end-tidal CO2?

A

35-45 mmHg

Values greater than 60 mmHG may warrant IPPV

51
Q

What do increased end-tidal CO2 indicate?

A

Alveolar hypoventilation
Increased cardiac output
Hyperthermia
Bicarbonate administration

52
Q

What do decreased end-tidal CO2 indicate?

A

Decreased cardiac output
Hyperventilation/shallow breaths
Artefact
Hypothermia

53
Q

What does anaesthetic agent concentration measure?

A

Inspired and expired concentrations
Helps in assessing depth
Need to know MAC of different agents
Useful when using very low flows in a circle system

54
Q

How can we assess oxygenation?

A

Clinically - cyanosis
Arterial blood gas analysis - intermittent results, invasive, possible complications
Pulse oximetry - continuous, non-invasive, measured at level of arterioles

55
Q

What does pulse oximetry give information on?

A

Arterial haemoglobin saturation
Pulse rate
Adequacy of tissue perfusion

56
Q

Why is saturation important?

A

Nearly all oxygen in blood is carried in combination with haemoglobin
Measurement of saturation enables estimation of oxygen content and oxygen delivery to tissues
Oxygen delivery equals oxygen content times cardiac output

57
Q

What is the normal SpO2 range?

A

95-100%
SpO2 less than 90% means a PaO2 less than 60mmHg
PaO2 less than 60mmHg defined as hypoxaemia

58
Q

What is pulse oximetry not a good measure of?

A

Ventilation

59
Q

When should you keep the pulse oximetry probe in place?

A

Until you know SpO2 can be maintained on air

60
Q

What should be done if SpO2 is low on 100% O2?

A

Check if value is true - check oxygen supply, check probe position, check BP, have you used an alpha-2 agonist?

61
Q

What is happening if SpO2 is low on 100% O2 and the value is true?

A

Increased right to left shunting of blood - anatomical, inrapulmonary
Impaired diffusion - very rare

62
Q

What does an ECG provide information on?

A

Electrical activity of the heart

Doesn’t tell us about - cardiac output, blood pressure, mechanical activity of the heart

63
Q

What is arterial blood pressure used to assess?

A

Adequacy of tissue perfusion - O2 delivery

64
Q

What may hypotension be due to?

A

Reduced CO
Reduced SVR
Commonest cause is reduced CO due to anaesthetic drugs or hypovolaemia

65
Q

What are the normal arterial BP values?

A

Systolic 100-160mmHg
Diastolic 60-100mmHg
Mean 80-120mmHg

66
Q

What value should arterial BP be kept above?

A

60-70mmHg otherwise renal perfusion will fall

67
Q

Describe a Doppler ECG

A

Accuracy dependent on cuff size
Cuff about level with heart
Measures systolic BP
Cats - value is between systolic and mean
Some recommend adding 14mmHg in cats for true systolic BP

68
Q

Describe oscillometry

A 
Accuracy dependent on cuff size
Cuff about level with heart
Gives SAP, MAP and DAP
Tends to under-read
MAP value is most accurate
69
Q

What should be done with invasive BP if blood pressure is low?

A

Keep mean BP above 60-70mmHg
Otherwise renal perfusion will fall
What shuold be done - reduce depth, fluid bolus, inotropes, avoid NSAIDs

70
Q

When are blood gases monitored?

A

If concerns about lung function during anaesthesia

71
Q

What can be gained from an arterial sample of blood gases?

A

Efficiency of ventilation

72
Q

What can be gained from venous samples of blood gases?

A

Acid-base status

73
Q

What infromation is given by blood fases?

A 
PO2
PCO2
pH
Oxygen saturation
HCO3-
BE
Electrolytes
74
Q

What does arterial O2 tension (PaO2) measure?

A

How well the lungs can oxygenate blood

75
Q

What is arterial CO2 tension (PaCO2) a measure of?

A

Alveolar ventilation

76
Q

What are the upper limits of PaCO2?

A

Values greater than 60 mmHg - may warrant IPPV

77
Q

How is core temperature most effectively measured?

A

Thermistor probe-oesophagus, rectum

78
Q

What patients are more at risk of hypothermia?

A

Smaller patients - increased surface area to body mass ratio

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